Oxidative Addition of Secondary Phosphine Oxides through Rh(I) Center: Hydrido-Phosphinito-Rh(III) Complexes and their Catalytic Activity in Hydrophosphinylation of Alkynes

The reaction of [Rh(μ-Cl)(cod)]₂ with diimines, differing in their steric and electronic properties, and with diphenylphosphine oxide leads to the oxidative addition products, hydrido-phosphinito-Rh(III) complexes {Rh(PPh₂OH)(PPh₂O)(NN)(H)Cl} (1), stabilized by the formation of a hydrogen bonded phosphinous acid-phosphinito quasi-chelate [(PO⋅⋅⋅HOP)-κ²P]. Exchange of hydride by chloride to afford {Rh(PPh₂OH)(PPh₂O)(NN)Cl₂} (2) occurs in hydrido complexes containing low steric hindrance diimines and is inhibited for complexes containing encumbered diimines. Complexes 1 react with BF₃⋅OEt₂ with exchange of the acidic proton by BF₂, and transformation of the quasi-chelating PO⋅⋅⋅HOP into a chelating PO-BF₂-OP ligand in {Rh{(PPh₂O)₂BF₂}(NN)(H)Cl} (3). The reaction of [Rh(μ-Cl)(nbd)]₂ or [Rh(acac)(nbd)] with diphenylphosphine oxide leads to coordinatively unsaturated nortricyclyl-phosphinito-Rh(III) complexes, {Rh(PPh₂OH)(PPh₂O)(ntyl)(μ-Cl)}₂ (4) or {Rh(PPh₂OH)(PPh₂O)(ntyl)(acac)} (6), respectively. Their reaction with BF₃⋅OEt₂ results in the corresponding {Rh{(PPh₂O)₂BF₂}(ntyl)(μ-Cl)}₂ (5) or {Rh{(PPh₂O)₂BF₂}(ntyl)(acac)} (7). Some of these new complexes have shown catalytic activity in hydrophosphinylation of alkynes, with {Rh(PPh₂OH)(PPh₂O)(NN)(H)Cl} containing encumbered NN being efficient and regioselective catalysts in the hydrophosphinylation of phenylacetylene with diphenylphosphine oxide to produce (E)-diphenyl(styryl)phosphine oxide.